In recent years, in order to increase the transmission capacity of an overall system, a method of evaluating reception quality and adaptively allocating resources based on the reception quality has been popularly used in a communication system. In particular, MIMO (Multiple Input Multiple Output) communication which uses a plurality of antennas for transmission and reception is known to be able to dramatically increase the transmission capacity of the system, when using an independent channel called an eigenpath by SVD (Singular Value Decomposition) scheme, by controlling transmission power and a modulation scheme of each path based on an eigenvalue of the eigenpath.
A scheme based on water filling principle is considered as the most suitable scheme of adaptive control of the MIMO communication, and methods to increase the transmission capacity of the system with an actual discrete modulation method have been actively studied. In addition, since a path with the smallest eigenvalue has low cost performance of transmission, a method to simply control without using the path at all has been considered.
However, a control scheme of the MIMO communication using such an eigenpath is known as being very sensitive and transmission characteristics are thus dramatically deteriorated if orthogonality is collapsed for some reason. In order to address such a problem, it is suggested to prevent the characteristic deterioration when orthogonality is collapsed, with a Doppler frequency and the likes as known information, by calculating SINR (Signal to Interference plus Noise Ratio) based on the information and performing control (see Patent Document 1).
FIG. 8 is a diagram illustrating a basic configuration of a conventional wireless communication system which performs adaptive control based on SINR. FIG. 9 is a flow chart illustrating an operation. A transmission apparatus 1 is provided with an S/P unit 31, an adaptive modulation and coding unit 32, an adaptive transmission power control unit 33 and a transmission beam forming unit 34, whereas a reception apparatus 2 is provided with a reception antenna processing unit 35, a demodulation processing unit 36, and a P/S unit 37. A channel estimation unit 38, an SVD unit 39, an SINR calculation unit 40 and a transmission adaptive control unit 41 may be provided to either the transmission apparatus 1 or the reception apparatus 2.
The channel estimation unit 38 performs channel estimation of a current propagation path (step 201), and the SVD unit 39 calculates a transmission weight by an SVD process from a channel estimation value (step 202). The SINR calculation unit 40 calculates SINR based on the known information of the Doppler frequency (step 203), and then the transmission adaptive control unit 41 performs adaptive control based on SINR (step 204).    Patent Document 1: Japanese Patent Application Laid-Open No. 2005-252834